Electrosurgical devices, and particularly probes for devitalizing tissue (ablation probes), are known which include a probe body with at least one electrode for applying a high-frequency current and a cooling device. The high-frequency current is generated via a high frequency generator.
In high-frequency surgery, an alternating current is passed through the human body at a high frequency in order to selectively damage tissue. One application of high frequency surgery is the devitalizing of tumor tissue. High frequency surgery utilizes the thermal effect of heating by which devitalizing of tissue is achieved.
A distinction is drawn between a bipolar and a monopolar application of the high-frequency current. In a monopolar application, the instrument of the electrosurgical device includes only one electrode, while a second, neutral electrode is placed directly on the patient. The current flows, in an inversely proportional relationship to the resistance in the tissue, from the electrode of the instrument to the neutral electrode. In the immediate vicinity of the electrode of the instrument, the current density is high enough for the described thermal effect to occur. With increasing distance from this electrode, the current density falls off in inverse square relation thereto. The devitalizing effect of the high-frequency current is therefore spatially limited.
With a bipolar application, the instrument includes two electrodes. For example, a probe tip can be configured as a first electrode, while a proximal section of the probe serves as the second electrode. The high-frequency current or high-frequency voltage is applied between the two electrodes, which are insulated from one another. The circuit is completed through the tissue that is situated therebetween. A current distribution field is produced which is concentrated in the immediate vicinity of the probe.
It is self-evident that, regardless of the start of application of the high-frequency current, a high field density forms in the immediate vicinity of the instrument. This high field density can lead to carbonization of the surrounding tissue. This carbonization is undesirable, at least in the devitalizing of tumors, since a layer formed in this way has a strongly insulating effect and hinders the treatment in deeper tissue regions. In addition, the body cannot readily decompose such carbonized tissue.
For this reason, the cooling device is used to cool the immediately adjacent tissue to prevent dehydration and/or carbonization of the adjacent tissue.
When devitalizing tumor tissues with the aid of an ablation probe, it can arise that adjacent structures (e.g. blood vessels, lymph ducts, organs), impair the current distribution, and thus the heat distribution, close to the probe. In the case of monopolar probes, the position of the neutral electrode relative to the probe or the instrument can lead to an unwanted current distribution within the tissue. It is thus desirable, for example, when treating tumors, to provide a heat distribution field that is as even as possible, and is preferably spherical, in order to devitalize the tumor completely.